Rotary blowers having rotors driven by timing gears disposed in a gear chamber partially filled with lubricating oil are well known in the art as may be seen by reference to U.S. Pat. Nos. 4,924,839 and 4,714,418. These patents are incorporated herein by reference. The gear chamber in U.S. Pat. No. 4,924,839 has a self contained oil supply for lubricating the timing gears and bearings open to the chamber in response to rotation of the gears. The timing gears, which are partially submerged in the oil, sling the oil about the chamber to effect the lubrication. Such slinging causes a rather fine air oil mist in the chamber. Attempts to employ conventional vents for the chamber to relieve pressure buildup in the chamber, as in U.S. Pat. No. 4,714,418, have caused loss of oil due to the fine oil mist flowing through the vent.